Apparatus and method for controlling a vibratory feeder in a weighing machine

Abstract

Apparatus and methods are shown for controlling a weighing machine in which product is fed into one end a vibratable pan of a vibratory feeder and is discharged from the other end, for example into a weigh bucket. In a first embodiment, the amplitude of vibration of a pan is measured and is compared to a desired amplitude. The measured amplitude is compared to a desired amplitude, and the amplitude of vibration is adjusted by modifying an input signal to a vibrator attached to the pan until the measured amplitude equals the desired amplitude. In a second embodiment, a mechanism is included to stop the loading of product into a pan when a predetermined amount of product has been discharged from a pan into a weigh bucket, and the weight of product in the pan is monitored as additional product is discharged into the weigh bucket Only a preselected additional weight of product is subsequently discharged into the weigh bucket. A third embodiment involves at least two pans arranged in series, and the weight of product in the downstream pan is determined and monitored. The measured weight is compared to a desired weight of product in the downstream pan, and the amplitude of vibration of the upstream pan is adjusted, as needed, in a closed-loop manner to feed more or less product into the downstream pan to establish and maintain the desired weight in the downstream pan.

What is claimed is: 
     
       1. An apparatus for controlling the feeding of product in a weighing machine from a product supply source into one end of a pan of a vibratory feeder, moving the product towards an opposite end of the pan as a vibrator drives the pan in response to an input signal, and discharging the product from the opposite end of the pan into a weigh scale, the apparatus comprising: means for temporarily stopping the feeding of product from the source into the pan of the vibratory feeder;   means for monitoring the weight of product in the pan of the feeder and for generating a signal indicative of the monitored weight when the feeding of product from the source has stopped; and   control means for stopping the vibratory feeder from discharging product from the opposite end of the pan into the scale when a change in the signal indicates a drop of the monitored weight by a predetermined value.   
     
     
       2. An apparatus as described in claim 1, wherein the weigh scale has a weigh bucket and generates signals indicative of the weight of product in the weigh bucket, and the control means also monitors the signal indicative of the weight of product in the weigh bucket for activating the means for monitoring when the signal indicative of the weight of product in the weigh bucket reaches a preselected value. 
     
     
       3. An apparatus as described in claim 2, wherein a sum of the weight of product corresponding to the signal indicative of the predetermined value and the weight of product corresponding to the signal indicative of the preselected value substantially equals a desired weight of product. 
     
     
       4. An apparatus as described in claim 1, wherein the weighing machine includes means for feeding product from the source into one end of a pan of an additional vibratory feeder, moving the product towards an opposite end of the feeder as an additional vibrator drives the additional pan in response to an additional input signal, and discharging the product into an additional weigh scale, the apparatus further comprising: means for temporarily stopping the feeding of product from the source into the additional vibratory feeder; and   means for monitoring the weight of product in the additional feeder and for generating a signal indicative of the monitored weight of product in the additional feeder when the feeding of product from the source is stopped and wherein the control means stops the additional vibratory feeder from discharging product from the additional pan into the additional scale when the change in the signal indicates a drop of the monitored weight of product in the additional vibratory feeder by a predetermined value.     
     
     
       5. An apparatus as described in claim 1, wherein the means for stopping the feeding of product from the source into the feeder stops the feeding of product into the feeder after a predetermined feeding period. 
     
     
       6. Apparatus as described in claim 1 wherein: the weigh scale has a weigh bucket and generates a weight signal indicative of the actual weight of product in the bucket; and   the control means is connected to receive the actual weight signal for determining the predetermined value from a desired weight of product in the bucket and the actual weight of product in the bucket.   
     
     
       7. A method for controlling the feeding of product in a weighing machine from a product supply source through a pan of a vibratory feeder, as a vibrator drives the pan in response to an input signal from a power source, and causes the product to be discharged from the pan into a weigh scale, the method comprising the steps of: temporarily stopping the feeding of product from the supply source into the pan of the feeder;   monitoring the weight of product in the pan and continuously generating a signal indicative of the measured weight of product in the pan after the step of temporarily stopping; and   stopping the feeder from discharging product from the pan into a scale when it is determined during the step of monitoring the weight of the product in the pan that a change in value of the signal indicates the weight of product in the pan has dropped by a predetermined value.   
     
     
       8. A method as described in claim 7, further comprising the steps of: measuring the actual weight of product in the bucket and generating signals indicative of the actual weight;   monitoring the signals indicative of the actual drop in weight of product in a bucket of the weigh scale; and   performing the step of stopping the loading of product into the vibrator when it is determined during the step of monitoring that the weight of product in the bucket is a preselected value.   
     
     
       9. A method as described in claim 8, wherein the sum of the weight corresponding to the preselected value detected during the step of monitoring the actual weight of product in the bucket and the weight corresponding to the predetermined value detected during the step of monitoring the signal indicative of the weight of product in the pan substantially equals a desired value. 
     
     
       10. A method as described in claim 8, further comprising the step of: adjusting the input signal to the vibrator after it is determined during the step of monitoring the signal indicative of the actual weight of product in the bucket that the signal indicative of the actual weight of product in the bucket is the preselected value.   
     
     
       11. A method as described in claim 7, wherein the weighing machine includes at least one additional vibratory feeder for feeding product from the source through another pan of the additional vibratory feeder, as an additional vibrator drives the additional pan in response to an additional input signal, and causes the product to be discharged from the pan into an additional weight scale, the method for further comprising the steps of: temporarily stopping the feeding of product from the source into the additional pan; and   monitoring the weight of product in the additional pan and for generating a signal indicative of the monitored weight of product in the additional pan after the step of temporarily stopping, and   stopping the additional pan from causing product to be discharged from the additional pan into the additional scale when the change in the signal indicative of the monitored weight of product in the additional pan indicates a drop in weight by a predetermined value.   
     
     
       12. A method as described in claim 11, wherein the step of stopping the feeding of product from the source into the feeder is performed after a predetermined feeding period. 
     
     
       13. A method as described in claim 7, further comprising the step of: dumping product from the weigh bucket after the step of stopping the feeder from feeding product from the pan into the scale.   
     
     
       14. A method as described in claim 13, further comprising the step of: resuming the loading of product into the pan during the step of dumping product from the bucket.   
     
     
       15. The method of claim 7 further including the steps of generating a signal indicative of the weight of product discharged from the pan into the weigh scale; and   determining the predetermined value, at which the discharging of product from the pan into the scale is stopped, from the signal indicative of the weight of product discharged into the weigh scale and a desired weight of product.   
     
     
       16. A method of controlling feeding of product in a weighing machine from a product supply source through a pan of a vibratory feeder as product is discharged from pan to a weigh scale, the method comprising the steps of: temporarily stopping the feeding of products from the supply source into the feeder pan; and thereafter   simultaneously measuring the weight of product in the pan and the weight of product in the weigh scale and determining the difference between the weight of product in the weigh scale and a desired weight of product; and then   monitoring the weight of product in the pan to determine the additional weight of product discharged from the pan into the weigh scale; and   stopping the discharging product from the pan into the weigh scale when the additional weight of product discharged into the weigh scale is equal to the difference.